The goal of this study is to understand the mechanisms of the auto-reduction of high- valent iron species in two different myoglobin species, horse heart and human, in order to uncover the structural features that regulate the corresponding oxidative protein damage. Myoglobin?s propensity to oxidatively damage lipoproteins is a particular interest in the molecular mechanism of atherosclerosis. The hypothesis is that proton and electron movements that regulate the auto-reduction can inform how we study oxidative damage in proteins and atherogenic lipoproteins. To test this assumption, the mechanism will be evaluated by determining three different features. The first aim will focus on probing the kinetic and thermodynamic parameters of the auto-reduction reaction for both Mb species using transient UV-visible absorbance spectroscopy and by varying temperature and pH conditions. The second aim is to identify the proton source necessary for auto-reduction of the high-valent iron species and determine if one or more different protons are important in regulating the mechanism at physiologically low pH (inflammation sites) and neutral pH(blood based environments) utilizing kinetic solvent isotope effects, proton inventories, and site directed mutagenesis. The third aim focuses on identifying the electron donor source within the protein utilizing radical traps, tandem mass spectrometry and cyclic voltammetry.